Scaling and root planing (SRP) is the standard treatment, aiming to mechanically reduce the number of bacteria present on the affected root surfaces. Representing a non-specific form of treatment to a non-specific infection, it has proven effective in most cases and short follow ups(Hill et al 1981, Pihlstrøm et al 1983, Lindhe et al 1984, Becker et al 1990, Kaldahl et al 1993). However, recurrence rate is fairly high, suggesting that these diseases are life-long traits. Also, a small - still significant - group of patients shows remaining inflammation and continuous destruction of periodontal support despite adequate oral hygiene and proper mechanical treatment (Lang et al 1986, Greenstein & Caton 1990, Walker et al 1993, Bragd et al 1987, Renvert et al 1990, Haffajee et al 1991, Grossi et al 1994, Slots and Rams 1991, Socransky and Haffajee 1992).